1. Field of the Invention
The present invention relates to a method and an apparatus for recycling a resin component, especially a coated or plated resin component.
2. Description of the Related Art
Due to the increasing interest in the environmental issues and reutilization of resources, scrapped car recycling has recently come to attract attention in the field of the car industry. In general, about 75% of the material of an automobile by weight is reduced to scrap iron and nonferrous metals for reuse by removing, and the remainder or about 25% is disposed as industrial waste. The waste contains about 30% of resin material by weight, along with fibers, rubber, and etc.
Typically, the material of a resin component, e.g., the skin of a bumper, is composed of a coating film W4 formed on a base W3 of a thermoplastic resin such as polypropylene, as shown in the sectional view of FIG. 6. Available resins for the material of the coating film W4 include thermosetting resins, such as amino polyester, amino acrylic, polyester-urethane and acryl-urethane resins. Being liquid before making, these resins can be given a crosslinked structure by baking finish. Since this structure is firm and tight, a coated resin bumper is excellent in chemical resistance, heat resistance, scuff resistance, weathe-proof and surface gloss.
If this recycled material is obtained by grinding and pelletizing this bumper without removing coating film pieces are mixed with the polypropylene material. In molding this material having the film pieces therein, the film pieces lower the fluidity of the molten resin, and subject the resulting molded article to molding faults, such as burning, weld-marks, bubbles, etc. The coating film pieces which are exposed on the surface of the molded article mar the external surface of the final product.
Since there are hardly any interactions between the coating film pieces and the polypropylene resin for use as a base resin, the film pieces rather constitute foreign matter, which worsens the mechanical properties of the molded article. For example, the impact strength of the recycled polypropylene material contaminatedi with the coating film pieces therein is about 80% of that of virgin polypropylene.
Accordingly, recycling the coated resin component requires removal of the coating film.
As described in Automotive Technology Vol. 46, No. 5, pp. 3-9, 1992 (compiled and issued by Japan Automotive Technology Association), methods of removing the coating film are classified into three categories, mechanical, physical, and chemical methods.
The mechanical removing methods include the shot blasting method, screen-mesh method and etc. In the shot blasting method, the coating film is removed by blowing abrasive powder against the surface by compressed air. In the screen-mesh method, a coated resin component is roughly ground, pulverized, fused, and then filtered through a mesh, whereby unfused coating film pieces are removed.
In the shot blasting method, the coating film is removed by friction, impact and etc., so that this method is highly safe from the toxicological or ecological point of view. According to this method, however, the removal of the coating film requires a long treatment time and its efficiency is low, and it is difficult to treat curved portions of the component, in particular. In the screen-mesh method, on the other hand, the coating film pieces are removed by filtering, so that this method also has high ecological safety. Also in this case, however, the treatment time is long, and the coating film removal efficiency is not satisfactory.
According to the physical removing methods, the coating film is removed by means of halogen-based solvents or various organic solvents, taking advantage of the infiltration of the solvent into the interface between the coating film and the base material and swelling of the film caused by the solvent. These methods, however, are poor in ecological safety and relatively low in coating film removal efficiency and treatment capability, and may possibly cause change of properties of the base material.
Since the mechanical and physical coating film removing methods are low in coating film removal efficiency, final products made from molded articles by these methods have poor external surface and mechanical properties, and the range of their application is limited.
The chemical removing methods include the organic-salt method in which the coating film is chemically decomposed and removed by cutting ether bonds in the vicinity of crosslinking points of the coating film resin by means of, for example, an ethanol mixed solution which contains organic salt.
This method has a problem of secondary treatment, such as waste water treatment, and its treatment efficiency is low. According to this method, moreover, the removal of a deposit from a plated resin product is subject to low efficiency and insufficient treatment capability, and it is hard to obtain high-quality recycled resin components.